Grand Mountain Adventure is one of the most chillback and satisfying game ever on mobile platform. While the free gives you some... easy mountain. The Premium gives you infinite replayability and it's so worth it!
Just look at it! The detail on the terrain, the realistic simulated tesselation when object passes the snow, the variable-soft dynamic shadows, really good global Illumination, and amazing list of post-processing used in this game is out of mobile game era. The quality is simply indistinguishable than other console releases.
And all that while being playable so well. I tried it on Snapdragon 870, at maximum possible graphics it can do 60fps without hitch. Although you might want to take it down a notch (maybe Max graphics at 30fps) so it won't drain your battery so much. I also tried on Exynos with 140K AnTuTu, which also run the game fine at 30fps lowest setting medium resolution. The quality is so fast but knowing the game works at such low-end is amazing already.
Like I said, it's chillback. Use two fingers, and just swipe swipe while enjoying the scenery. Or y'know, being super competitive and get all gold medals and unlock double diamond all the way. The point is UP TO YOU. Do what you want! It's something you can rely on when you need a quick relaxation.
This is where free version differs a lot from the plus (pass) version. Because you opened a lot of mountains. Also the requirements are so much lower, which means you can explore more mountains and area easily without having to finish all challenges at 3 stars or something.
This is, by far, the best reason to get the premium version of this game. This really gives you all the Wonderlands version (that released on other platforms and consoles) in mobile. Which I think isn't that expensive to begin with. Or play smart and subscribe to Play Pass instead. Up to you really. Or just play the free version (but I assure you you'll crave those mountains you saw on my video gameplay right? Just look at those detailed new world)
Conclusion:
You must've heard how good this game is. Just buy it if you want to play this game for 8 hours and still getting new contents. The free is nice, but it feels like a demo. So... Yeah buy the premium.